With the push for everything organic, gardeners are looking for more sustainable ways to fertilize and care for their gardens. Recycling and composting is an effective way to not only save money, but to consume fewer resources and help the environment. A sometimes overlooked resource right in most kitchens is coffee. Coffee can provide needed nutrients such as nitrogen to plants if used correctly.
Nutrients in Coffee
Coffee grounds are a low-level nitrogen source. Their fertilizer value is approximately 2.0-0.3-0.2--with nitrogen being the highest value, the first number in the NPK (nitrogen, phosphorous, potassium [potash] value). Nitrogen is between 3 and 4 percent of what plants are made of, so they are in constant need of replenishing this nutrient.
Acidic or Not Acidic
Although coffee is acidic, the spent grounds are not, according to Oregon State University. It says the acid in coffee is water-soluble, so once it has been brewed, most of the acid has been soaked out of the grounds, and they are very close to pH neutral at 6.5 to 6.8 pH. This is in some dispute among gardeners, who through the years have considered coffee grounds to be acidic and praise their values for using on acid-loving plants such as azaleas, hydrangeas, tomatoes and blueberries. Rosie Lerner, horticulturalist at Purdue University, suggests erring on the side of caution and using coffee and coffee grounds only on acid-loving plants or spreading out coffee through an entire garden at about 10 dry pounds of grounds per 1,000 square feet. She adds, though, that the acidic properties of coffee grounds are no more than that of peat moss.
Composting with Coffee
Adding coffee grounds to a compost pile is one way to add substantial benefit to the composted materials. The carbon to nitrogen ratio in coffee grounds is about 20:1, so adding them as a green material is recommended. Mix them in the compost bin with brown materials such as dried leaves and shredded paper to keep the compost balanced. It is recommended that up to 25 percent of a compost pile's materials can be coffee grounds.
Shelf Life of Coffee Grounds
Coffee grounds do not spoil, so if you should find yourself with an abundance, simply store them in a container with a tight seal and use them as needed. If possible, dry them out as much as possible before sealing them into an air-tight container.
How to Use Coffee on Plants
Spreading the coffee grounds in a thin layer over the ground throughout the garden is often a recommended way to use them. Oregon State University suggests this as well as using a thin layer under a layer of mulch, which allows the coffee to decompose naturally over time and release nitrogen directly into the soil around the plants. It also suggests mixing them into the soil--this can be done before planting, when the ground is tilled in the beginning of the season. If this method is used, add some nitrogen-rich fertilizer as well so the plants can have the immediate benefit of the fertilizer in the beginning of the process before the grounds have started to decompose and release nitrogen into the soil.
Where to Get Coffee
What should a gardener do if they and their family do not drink enough coffee to support their garden? Many coffee shops will be happy to let you pick up and take home used grounds, usually free of charge. There are many other sources of free coffee grounds. Some gardeners ask their neighbors to save them; others bring discarded coffee grounds home from work or ask neighboring restaurants or convenience stores.